1. Field of the Invention
The present invention relates to a liquid outflow control unit capable of controlling the flow rate of the injected liquid and used in a continuous liquid injector or the like for sequentially injecting into a desirable portion of a human body a liquid such as a liquid medicine accommodated within a liquid accommodating portion. 2. Description of the Related Art
In one of conventional methods of continuously injecting a liquid such as a liquid medicine into a human body, a liquid accommodated in an injector is manually or automatically supplied into the body through a needle or a catheter. In another method, a liquid in an instillator is naturally or automatically supplied into the body.
Such continuous injection of the liquid takes a few minutes or a few hours. During that time, a needle or the like is connected continuously to a syringe or the like, and this may cause pain to the patient or limit his or her actions during the injection. It may also be necessary for the operator, who may be a doctor or a nurse, to hold a syringe or check the amount of liquid given by an intravenous drip injection, making the injection procedure a troublesome task.
Accordingly, a small-sized easy-to-handle continuous liquid medicine injector (or catheter) which does not confine the actions of a patient or an operator has been proposed (for example, in Japanese Patent Laid- Open No 56-102252 and its corresponding U.S. Pat. No. 4,318,400, Japanese Patent Publication No. 61-51901 and Japanese Patent Laid-Open Nos. 62-11464 and 62-11465).
All of these conventional continuous liquid medicine injectors therein incorporate a balloon or a bag made of an elastic material. An inlet from which a liquid medicine is put into the balloon is provided in one end of the balloon, and an outlet from which the liquid medicine is forced out of the balloon is provided in the other end of the balloon. The inlet is provided with a check valve which allows the liquid medicine to flow into the balloon but does not permit it to flow out of the balloon. In such arrangement, the liquid medicine accommodated in the balloon is forced out of its outlet due to the contraction of the balloon against the human body through an instrument such as a needle inserted into the body.
However, all of these continuous liquid medicine injectors involve the problem that the flow of liquid medicine cannot be controlled sufficiently in the outlet. This has been a big obstacle to practical use of these injectors.
The outflow control of a liquid medicine in Japanese Patent Laid-Open No. 56-102252 is provided by a very thin flow control element provided in a fluid path (mouth) which fluid communicates between the inside and outside of the balloon. The flow control element includes a somewhat short linear pipe. A change in the flow is considered to be performed by changing the length and inner diameter of the pipe although they are not specifically described. However, it is considered to be virtually impossible to increase the length of the flow control element sufficiently because it is incorporated in the flow path and also to extremely reduce the inner diameter from a standpoint of manufacture. Thus, although a liquid medicine is required to be supplied in very small amounts to the human body for a long time depending on the kind of the medicine, the flow control element cannot sufficiently satisfy such requirement.
More specifically, in Japanese Patent Publication No. 61-51901, the flow of liquid medicine is controlled by suitably changing the diameter of through holes formed in the wall of the tube-like body on which the balloon is mounted or by employing a diaphragm which varies the area of the inner diameter of the outlet in the tube-like body in accordance with the inner pressure of the balloon. However, control of the diameter of the through hole formed in the tube wall does not ensure sufficient control of the flow rate due to the thinness of the tube wall. Also, the required diaphragm is difficult to manufacture and hence unsuitable for mass production, and its use is, therefore, not practical.
Furthermore, in the injector proposed in Japanese Patent Laid-Open No. 62-11464, control of the flow of liquid medicine is provided by varying the diameter of a thin tube (thin hole) formed so as to extend axially of the tube wall of a catheter. However, the formation of a thin axial hole in the thin catheter is difficult in itself, making precise control of the flow rate more difficult.
Furthermore, the injector proposed in Japanese Patent Laid-Open No. 62-11465 incorporates therein a liquid flow regulating valve in the liquid outlet, and flow control is provided by controlling the restricting ratio of the flow regulating valve. However, precise control is also difficult in this injector.
An object of the present invention is to provide a liquid outflow control unit which has a simple structure and which ensures precise control of the outflow of liquid.